1. Field of the Invention
This invention relates to a balloon catheter used primarily in medical treatment and surgery for the purpose of dilating lesion sites such as strictures or blockages in passages in the body, and more particularly to a balloon catheter, and method for manufacturing a balloon catheter, used in percutaneous translumin angioplasty (PTA) or percutaneous translumin coronary angioplasty (PTCA), which are treatments for dilating lesion sites such as strictures or blockages in coronary arteries, extremital arteries, kidney arteries, and peripheral blood vessels, etc.
2. Description of the Related Art
The common balloon catheter is formed by joining a balloon that is expanded and contracted by adjusting the internal pressure therein to the distal end of a catheter shaft, wherein, in the interior of the catheter shaft, are formed, extending in the axial direction thereof, a lumen (guide wire lumen) for inserting therein a guide wire, and a lumen (inflation lumen) for passing a pressurized fluid that is supplied for adjusting the inner pressure in the balloon. Using such a balloon catheter as this, angioplasty is performed according to the procedure now described. First, the guide wire passed through the guide wire lumen is made to pass through the stricture or other lesion site, the balloon is inserted into the body along that guide wire and made to coincide with the lesion site, a pressured fluid such as a suitably diluted shadow-casting agent is supplied through the inflation lumen to the balloon, the balloon is caused to expand, and the lesion site is subjected to dilation therapy. After the lesion site has been subjected to the dilation therapy, the balloon is first made to contract by reducing the pressure therein and folded, and then removed from the body, whereupon the angioplasty is finished.
Such balloon catheters as these are divided into two types, namely in over-the-wire type balloon catheter wherein a tube 200 for passing the guide wire is deployed so that it reaches from an adapter member 202 connected to the base end of the catheter shaft 201 to the distal end of the balloon 203, as exemplified in FIG. 27, and a rapid exchange type balloon catheter wherein a tube 210 for passing the,guide wire is deployed so that its reach is limited from midway along the catheter shaft 211 to the distal end of the balloon 212, as exemplified in FIG. 28. In FIG. 27 and 28, the distal part containing the balloon is represented slightly enlarged over the near portion to facilitate understanding.
The over-the-wire balloon catheter diagrammed in FIG. 27 is configured with a catheter shaft 201 formed by the joining of a tube 204 on the distal side and a tube 205 on the proximal side, a balloon 203 joined to the distal end of the tube 204 on the distal side, and the adapter member 202 joined at the base end of the tube 205 on the proximal side.
The structure of the distal part of such a balloon catheter is exemplified in FIG. 29(a). The guide wire passing tube 200 having a guide wire lumen 200a is passed through the inner space of the balloon 203. The inner circumferential surface of a sleeve part 203a on the distal side of this balloon 203 and the outer circumferential surface of the guide wire passing tube 200 are joined concentrically with an adhesive 206. And the inner circumferential surface of a sleeve part 203b on the proximal side of the balloon 203 and the outer circumferential surface at the distal end of the outside tube 204 are joined concentrically with an adhesive 207. Symbol 208 in this figure designates a radiopaque marker. Also, as diagrammed in the A1-A2 cross-section in FIG. 29(b), the guide wire passing tube 200 and outside tube 204 are deployed concentrically, and an inflation lumen 209 for passing the pressurized fluid supplied to the balloon 203 is formed between the inner surface of the outside tube 204 and the outer surface of the guide wire passing tube 200. Although, in this example, the guide wire passing tube 200 and outside tube 204 are deployed concentrically, there are also configurations wherein the outer circumferential surface at the distal end of the guide wire passing tube 200 is bonded securely to the inner surface of the outside tube 204 so that the guide wire passing tube 200 will not move backwards relative to the outside tube 204 such that the relative position therebetween shifts greatly.
There is also another distal part structure, such as exemplified in FIG. 30. According to FIG. 30, a guide wire passing tube 214 configuring a guide wire lumen 214a and an inflation tube 210 configuring an inflation lumen 210a are deployed in parallel. As diagrammed in the B1-B2 cross-section in FIG. 30(b), both tubes are secured by a heat-shrunk tube 215 to configure a catheter shaft 211. Also, the inner circumferential surface of the sleeve part 212a is bonded to the outer circumferential surface on the distal end of the guide wire passing tube 214 with an adhesive 216, and the inner circumferential surface of the sleeve part 212b on the proximal side of the balloon 212 and the outer circumferential surface of the catheter shaft 211 are bonded with an adhesive 217. The symbols 218A and 218B in this figure indicate radiopaque markers. There is yet another distal part configuration, such as that diagrammed in FIG. 31. In the C1-C2 cross-section in FIG. 31(b) is diagrammed a catheter shaft 211 consisting of a single-structure tube-shaped member 219 comprising a guide wire shaft 214 and inflation lumen 219a internally.
The rapid exchange type balloon catheter diagrammed in FIG. 28, on the other hand, has a catheter shaft 211 comprising a tube shaped member, configured such that the balloon 212 is joined to the distal end of that catheter shaft 211, the adapter member 213 is joined to the base end of the catheter shaft 211, and a guide wire passing tube 210 also deployed in the distal part.
In general, in the interest of smooth insertion into a passage in the body and reaching the most distant site along that internal passage, balloon catheters having smaller outer diameters are advantageous. That being so, unused balloon catheters are commonly provided in a condition wherein the balloon has been made to contract under reduced pressure and folded up to minimize the outer diameter of the balloon.
The properties required as minimal limitations in such balloons are (1) that they be able to withstand pressures sufficiently so that they do not burst when the inner pressure is increased by a pressurized fluid, (2) that they exhibit a predetermined relationship between the expanded outer diameter and the expansion pressure (expansion characteristics), and (3) that the strength of the balloon in the circumferential direction and axial direction be calculated in a balanced manner so that the balloon can exhibit deformation so as to conform to winding internal passages when expanded. It is also preferable that the skin thickness of the balloon itself be as thin as possible in order to make the outer shape of the balloon small when it is folded up.
Balloon catheters, moreover, are often used a number of times for the same lesion site. In such cases, from the perspective of reintroducing the balloon catheter, it is important that the balloon exhibit the property of being able to retain well the condition wherein it is made to contract under reduced pressure and folded up (folded shape retention characteristics). Also, the skin thickness of the straight tubular part of the balloon should be as thin as possible so that it has a small outer diameter in the folded condition, and the skin thickness in the conical parts or sleeve parts of the balloon should also be as thin as possible, for the same reasons, but also to realize good reintroduction performance toward the lesion site when reused. That the balloon exhibit good fold-up retention, thin skin in the straight tubular part, and thin skin in the sleeve parts is equally important from the perspective of retracting the balloon easily from the internal passage after the lesion site has been subjected to dilation therapy.
However, conventional balloon catheters are inadequate, for the two reasons stated below, in terms of their performance in being reintroduced to a lesion site and in terms of the ease of retracting the balloon from the internal passage following dilation therapy. The first reason is that, although the balloons are subjected to a heat treatment to cause them to remember and retain the condition wherein they are folded up, it is very difficult to maintain the folded condition retention properties and memory properties in these balloons. The balloon is formed from a polymer material, and therefore is inferior in terms of shape retention and shape memory, and that shape retention and shape memory are the more lost the higher the internal pressure to which the balloon is subjected during treatment is made. The shape retention and shape memory of the balloon are largely dependent on the material of which the balloon is made and the skin thickness thereof. As that skin thickness is made thinner, shape retention and shape memory decline very rapidly. When the shape retention and shape memory of the balloon have declined, after it has been expanded, it will not return to a folded condition even when made to contract but, as diagrammed in the side elevation in FIG. 32(a) and the D1-D2 cross-section in FIG. 32(b), the balloon 220 joined to the guide wire passing tube 221 and outside tube 222 form flat wings 220a and 220b, the outer diameter of the balloon 220 takes on maximum width, and, simultaneously, the controllability of the balloon catheter declines markedly due to the hard wings 220a and 220b. Accordingly, a design is desired wherewith, after insuring satisfactory basic performance in the balloon, the balloon configuring material can be made as pliable as possible, with the skin thickness made thin, so that, even if wings are formed in the balloon, the controllability thereof can be prevented from declining. Conversely, however, when the highest priority is placed on balloon folded shape retention and shape memory, and the balloon skin thickness is made thicker than necessary, the folded shape thereof does not stabilize, the sleeve parts of the balloon become thick at the same time, and it becomes markedly more difficult both to reinsert the balloon to the lesion site and to retract the balloon from the internal passage after treatment.
The second reason is that, when the balloon is caused to contract by reducing the pressure therein, wrinkles 223 are formed in the outer surface of the balloon 220 wherein wings 220a and 220b have formed, in an angular direction that is at right angles to or nearly at right angles to the axial direction of the catheter. When the balloon contracts in this condition with the wrinkles 223 developed therein, it becomes easier for the wings described above to form, and, at the same time, the wrinkles function just like a framework, and the wings are readily formed in a flat shape, as diagrammed in FIG. 32(b). The primary cause of the development of such wrinkles is that the relative deployment relationship between the guide wire passing tube and the balloon is not maintained as it should be. In a balloon catheter structured such that the guide wire passing tube 200 is deployed concentrically inside the outside tube 204, as diagrammed in FIG. 29, for example, when the balloon catheter is being pushed ahead inside an internal passage and advanced to a lesion site, when a resistance force is encountered at the leading end of the balloon catheter, that resistance force acts on the tip 200b of the guide wire passing tube 200, and the guide wire passing tube moves backward relative to the outside tube 204. Thereupon, the balloon 203 can do nothing but absorb the positional discrepancy between the two tubes, resulting in wrinkles forming in the balloon 203. When the balloon 203 is expanded with a high pressure, the balloon 203 extends in the axial direction, but, at the same time, a pulling force in the axial direction also acts on the guide wire passing tube 200 that is passing through the interior of the balloon, whereupon the guide wire passing tube 200 is pulled out from the outside tube 204 on the distal side. When the balloon 203 is made to contract under reduced pressure in this condition, there is too much length in the guide wire passing tube 200 inside the balloon 203, and the guide wire passing tube 200 can do nothing but effect a snaking movement. As a result, the ability of the guide wire to pass through declines, the refolding properties decline, and the wrinkles described above develop. Such a phenomenon as this can occur in the balloon catheters diagrammed in FIG. 30 and FIG. 31 as well as in the balloon catheter diagrammed in FIG. 29. More specifically, with the balloon catheters diagrammed in FIGS. 30 and 31, because the guide wire passing tube and inflation tube are joined, when the balloon is expanded under high pressure, the guide wire passing tube extends inside the balloon, and, when the balloon is made to contract under reduced pressure, there is too much length in the guide wire passing tube, and snaking results.
In the foregoing, the structure demanded in the far portion of the balloon catheter containing the balloon, and the problems therewith, are described, but good following or conforming properties and controllability are demanded in a balloon catheter so that the manipulations of a technician on the base end are communicated well to the leading end of the balloon catheter. Therefore, the catheter shaft of a balloon catheter is commonly configured such that tubular members are connected, using a comparatively flexible tubular member in the far portion and a tubular member that is stiffer than that of the far portion in the near portion. However, when tubular members having different rigidity are connected together, there is a strong likelihood that breakage or bending will occur at that connection, a likelihood that is particularly strong in slender structures like catheters. That being so, tubular members having extremely different rigidity are not used, and it has been necessary to effect such measures as (1) to connect a plurality of tubular members having gradually different rigidity in multiple stages, (2) to reinforce the connection between the tubular members using a reinforcing material, or (3) to use a tapered tubular member wherewith the rigidity is made to continuously vary. When a plurality of tubular members having gradually different rigidity are connected in multiple stages, a material limitation arises per force in that a material exhibiting rigidity close to that required must be selected. This is a problem in that, as a result, it is difficult to secure the desired controllability. When the tubular member connections are reinforced with a reinforcing material, great care must be taken with respect to the dimensions of the reinforcing material so that the outer diameter of the catheter is not made too large by that reinforcing material and so that interior space (for the lumens, etc.) can be adequately secured. In addition to that, in some cases, the bond between the reinforcing member(s) and the stiff tubular member on the proximal side becomes very hard and catheter controllability declines. The method of using a tapered tubular member and continuously varying the rigidity thereof is an excellent method, but requires an enormous amount of labor to fabricate the tapered tubular member, and it is difficult to fabricate products of stable quality.
Now, conventionally, as means of enhancing the controllability of balloon catheters, and particularly the controllability when the balloon catheter is passed through winding internal passages, methods have been employed such as applying a coating to the far portion of the catheter, using a lubricant consisting of silicon oil or a fluorine resin, or applying a hydrophilic coating that can activate the surface so that it is lubricated when wetted. A hydrophilic coating is particularly beneficial from the standpoint of durability and low friction relative to winding internal passages. The method almost always adopted in hydrophilic coatings capable of activating the surface so that it is lubricated when wetted is that of forming a surface by bonding polymer materials exhibiting water solubility or hydrophilia, and derivatives thereof, to a base material on the surface constituting the target. When this method is applied to the distal part of a balloon catheter, the hydrophilic coating will also be applied to the balloon. However, in order to secure good controllability and good advancing properties in the internal passage, the balloon should be administered in a state wherein it has been conditioned to fold-up. When the hydrophilic coating described above is applied to such a balloon, the hydrophilic coating acts just as an adhesive, whereupon the balloon clings in the folded state, so that the balloon becomes incapable of expanding. This problem is caused by moistening when the catheter is subjected to ethylene oxide gas sterilization or by the moisture in the atmosphere when in storage, and develops when the water soluble or hydrophilic polymers configuring the hydrophilic coating exhibit adhesion, and the surfaces of the folded balloon that have been given the hydrophilic coating contact each other and stick to each other. Also, when surfaces that have been given a high-density hydrophilic coating stick to each other, there have been times when the coating peels off. In order to suppress these problems, it is necessary to lower the density of the hydrophilic coating administered to the balloon. When the density of the hydrophilic coating is lowered, however, adequately low friction properties cannot be imparted to the catheter surface, making it very difficult to secure good controllability in winding internal passages, which was the original objective.
Conventionally, moreover, hydrophilic coatings have been applied only to the far portions of balloon catheters, but t here are cases where, in actual use, performance is greatly affected not only by the friction between the catheter and the internal passage, but also by friction between the catheter and other items used together therewith, such as treatment instruments. The procedure used when performing vasodilation therapy on coronary arteries is described below as an example. The balloon catheter is led into the coronary artery through a guiding catheter that is first deployed from a femoral artery or humeral artery, through the aorta, to the vicinity of the entrance to the coronary artery. The guiding catheter, however, is formed so as to be bent in a particular shape, so that the leading end of the guiding catheter on the distal side, and the leading end orifice thereof, can be more easily deployed at the entrance to the coronary artery, in view of the fact that the aorta bends sharply at the aortic arch.
When the balloon catheter encounters intense friction at the bent portion of the guiding catheter, and particularly when the comparatively stiff proximal-side tube of the balloon catheter is located in that bent portion, the controllability of the balloon catheter declines markedly. Also, when the outer diameter of the proximal-side tube configuring the catheter shaft is larger than the tube on the distal side, the friction becomes great between the large diameter portion of that proximal-side tube and the bent portion of the guidance catheter, and the controllability of the balloon catheter declines markedly.
There are also cases, relating to a different phenomenon than that described above, where, when treating lesions at vascular branches or branching lesions, multiple balloon catheters are simultaneously passed through the same guidance catheter and deployed in the coronary artery. The friction naturally becomes great between the balloon catheters and the guidance catheter or between the balloon catheters themselves during such procedures, whereupon the controllability of the balloon catheters deteriorates. This phenomenon is also now a problem. In a recent trend, moreover, guidance catheters of smaller diameter are being used in an increasing number of cases due to the increase in the use of approaches from the humeral artery. More specifically, there is a gradually increasing trend in the use of the 6 Fr size over the conventional 7 or 8 Fr size. This means that the trend is toward increasing the friction with the balloon catheter that is passed therethrough. It also means, in cases where the outer diameter of the near-portion tube is larger than the outer diameter of the far-portion tube, that the friction between the near-portion tube and the small-diameter guidance catheter will become greater.
Also, various materials are being used for the catheter shaft, depending on the performance demanded, but synthetic resin materials which combine flexibility and machinability are used most widely. However, in cases where it is particularly desired to make the configuration stiff on the technician""s end, as described in the foregoing, and in cases where it is desired to prevent squashing by pressure from internal tissue or treatment instruments used concurrently, a tubular member made of metal has been used as part of the configuring material of the balloon catheter. When a metal tubular member is used as a configuring member of the balloon catheter, however, the metal is generally readily susceptible to plastic deformation, and a residual bending tendency is readily assumed, wherefore, once a deformation has been imparted for some reason, the bent condition becomes perpetuated. As a result, many cases have been observed where the balloon catheter could not thereafter be used, or the controllability thereof deteriorated markedly.
Next, the conventional balloon and the problems therewith are described. As described in the foregoing, the properties required as minimal limitations in balloons include, (1) that they be able to withstand pressures sufficiently so that they do not burst when the inner pressure is increased by a pressurized fluid, and (2) that they exhibit a predetermined relationship between the expanded outer diameter and the expansion pressure (expansion characteristics). The expanded outer diameter relative to each nominal pressure determined within a range extending roughly from 4 atmospheres (approximately 0.4 MPa) to 10 atmospheres (approximately 1 MPa) is called the xe2x80x9cnominal expanded diameter.xe2x80x9d When using a balloon catheter, a suitable balloon is selected according to the diameter of the internal passage at the treatment site, giving consideration to the nominal expanded diameter and the expansion characteristics. As described earlier, it is better if the balloon skin thickness is thin, and it is particularly important that the tip of the balloon catheter that becomes the leading end have a small outer diameter and be flexible in order to pass through internal passages of high curvature and pass ahead of lesion sites that are highly constricted or occluded. Also, the tip is generally formed such that it is fused or bonded concentrically to the guide wire passing tube and the sleeve part on the distal side of the balloon, but, irrespective of the bonding or fusing, it is obvious that the tip will have a narrower diameter and be more flexible the thinner the skin thickness of the distal-side sleeve part.
Balloons of various nominal expanded diameters are usually provided in accordance with the diameters of the internal passages. In the manufacture of such balloons, in order to manifest the ability to withstand pressure and accurate expansion characteristics expected in the balloon, tubular members (parisons) having a predetermined shape for each nominal expanded diameter are prepared, and stretching processing is performed with magnitudes corresponding to the nominal expanded diameters. For most of those stretching processes, a blow molding method is adopted wherein metal molds are used which have cavities corresponding to the nominal expanded diameters. Thus, when the balloon is formed with the nominal expanded diameter as a reference criterion, (1) it is necessary, in order to secure pressure withstanding performance, to make the skin thickness of the straight tube portion of a balloon of large nominal expanded diameter slightly thicker than in a balloon of small nominal expanded diameter, and (2) it is necessary to make the skin thickness of the tubular member that constitutes the raw material synergistically greater because, as the nominal expanded diameter becomes greater, the amount of stretching increases. Accordingly, when the skin thickness of the tubular member is increased as the nominal expanded diameter is made larger, the skin thickness of the straight tube part of the balloon increases, while the skin thickness in the sleeve parts becomes extremely thick, thicker than the skin thickness of the straight tube part where there is only a small factor of stretching in the circumferential dimension, whereupon both diameter narrowing and flexibility are lost. When high-strength material is used, on the other hand, the skin of the straight tube part can be made thin, and the skin thickness of the sleeve parts naturally also becomes thinner to some extent, but, because the high-strength material is used, the sleeve parts are rigidly hard, whereupon flexibility is lost. If follows that there is room for improvement in terms of balloon strength to withstand pressure, and the balance between the skin thickness of the straight tube part and the skin thickness of the sleeve parts.
Also, as described earlier, in order to realize good controllability in winding internal passages and good transiting characteristics at highly constricted lesion sites, as required in a balloon catheter, it is important to make the diameter of the tip of the balloon catheter smaller and to enhance flexibility. For that reason, even more diameter narrowing and flexibility enhancement in the distal-side sleeve part that forms the tip are strongly desired. However, when balloons are formed using the blow method, it is necessary to use resin materials having intermolecular forces suitable to blow molding, and there are often limitations on the fluidity of the resin material during molding, wherefore it has been very difficult to freely make the skin thickness of the sleeve part thinner.
To date, a number of methods have been developed relating to effecting thinner skin thickness and high strength in balloons. In Japanese Patent Application Laid-Open No H3-37949/1991 (title of invention: xe2x80x9cThin-Skin, High-Strength Balloon and Manufacture Thereofxe2x80x9d), a balloon made from polyethylene terephthalate (PET) is disclosed. This balloon realizes thin skin and high strength, and excels in dimensional stability. Nevertheless, it suffers the shortcomings of lacking flexibility and being susceptible to pinhole failure. With pinhole failure, in particular, if the balloon fails inside a blood vessel, the vascular wall is subjected locally to high stresses, and there is an extremely high danger of damaging the vascular wall, wherefore this is undesirable.
In Japanese Patent Application Laid-Open No. H7-178174/1995 (title of invention: xe2x80x9cBase Tube and Balloon Catheterxe2x80x9d), moreover, a balloon is disclosed wherein thinner skin and higher strength are realized, and dimensional variation during expansion is suppressed, by fiber-reinforcing the base tube. With this method, however, the base tube becomes a three-layer structure, making it very difficult to achieve skin thickness thinning, particularly in the base tube of a balloon of small diameter, as a result whereof it is very difficult to form a balloon having a thinner skin thickness. In other words, this can hardly be called an ideal method for realizing the thin-skin balloons currently demanded where medical treatments are performed. The fact that the method of fabricating the base tube is complex presents a further problem in the production area.
As means for effecting both thinner skin and high strength in balloons, furthermore, balloons are made multi-layer using multiple polymer materials. In Japanese Patent Application Laid-Open No. H9-164191/1997, for example, a multi-layer balloon is disclosed wherein are used flexible polymers exhibiting an elongation at the break point near that of high-strength polymers. And in Japanese PCT Patent Application Laid-Open (KOHYO) No. H9-506008/1997, a balloon is disclosed that is based on a combination of a thermoplastic elastomer and a non-flexible-structure polymer material. In these multi-layer balloons, balloons are realized that exhibit high strength while retaining flexibility, but peeling between the respective layers is a worry. Compared to a single-layer tube, moreover, the process of extruding a multi-layer tube is generally more complex, which gives rise to problematic cost disadvantages.
As is evident from the examples of the prior art described in the publications noted above, while the disclosed balloon manufacturing methods do impart outstanding characteristics to the balloon, they nevertheless cause other problems, and hence cannot be called completely satisfactory methods.
An object of the present invention, in view of the several problems noted in the foregoing, is to provide a balloon catheter and method for manufacturing same wherewith (1) when the balloon is made to contract under reduced pressure and put in a folded condition again, after a lesion site has been subjected to dilation therapy, wrinkles are prevented from occurring in the balloon by favorably maintaining the folded shape retention and shape memory of the balloon, and favorably maintaining the relative deployment relationship between the balloon and the guide wire passing tube that passes through the interior of the balloon, (2) outstanding controllability is exhibited because well-balanced rigidity is effected from the proximal part to the distal part of the catheter shaft, (3) stickiness does not occur in the balloon in the folded condition even when a hydrophilic coating is applied to the far portion of the catheter, within a prescribed range, and adequate wear resistance is imparted thereto, (4) in cases where a tubular member made of a metal is used as a catheter shaft configuring member, performance deterioration is not brought about by plastic deformation in the metal tubular member, (5) a balloon is realized wherein the diameter thinning, and flexibility of the tip of the balloon catheter can be enhanced while retaining adequate ability to withstand pressure, and (6) a balloon is realized wherewith it is possible to make the skin thinner while retaining adequate ability to withstand pressure, and which exhibits flexibility such that insertion to a bent lesion site is made easy.
In order to achieve the object stated above, a first invention is a balloon catheter for use in therapy and surgery the purpose whereof is a dilation operation, configured with a balloon deployed on the distal end of a catheter shaft, comprising tension generation means for generating a tension in the axial direction of the balloon.
Here, it is desirable that there be a guide wire passing tube that passes through the interior of the balloon at the distal part of the catheter and that joins the distal end of the balloon, and that a tension be generated in the axial direction of the balloon by the application of a force in the axial direction at the distal part of the guide wire passing tube by means of the tension generation means.
It is also permissible to first join a non-tensioned guide wire passing tube to the distal end of the balloon and then assemble the balloon catheter in a condition wherein a force is applied in the axial direction to the distal part of that guide wire passing tube by the tension generation means.
A second invention is a balloon catheter for use in therapy and surgery the purpose whereof is a dilation operation, configured with a balloon deployed on the distal end of a catheter shaft, comprising a function for suppressing the generation of wrinkles oriented at angles perpendicular or nearly perpendicular to the axial dimension of the balloon when the balloon is caused to contract after expansion.
For the tension generation means described above and for specific means for realizing the wrinkle generation suppression function described above, it is preferable to use an elastic body that is incorporated in the interior of the balloon catheter. A favorable specific example of this elastic body is a coiled elastic body made of metal or the like.
It is also permissible that the balloon catheter have an elastic force transmitting body inside it that is supported by the elastic body, whereby a tension is imparted to the balloon in the axial direction through that elastic force transmitting body.
Furthermore, it is preferable that the elastic force transmitting body noted above comprise, as a configuring component, a linear member that extends to the vicinity of the balloon. It is also preferable that at least a portion of the linear member exhibit a tapered shape.
Another favorable configuration is one wherein the linear member is joined to one end of the coiled elastic body, and is deployed so as to extend from the interior of that coiled elastic body to the balloon.
It is also desirable that the stress generated by displacements in the elastic body be adjusted to within a range of 5 gf to 200 gf, inclusively, but preferably within a range of 10 gf to 50 gf, inclusively, in order to generate the desired tension in the balloon. By xe2x80x9cstressxe2x80x9d here in the present invention is meant the force (in units gf) that acts, when an elastic body is displaced, in a direction opposite the direction of that displacement.
The catheter shaft noted above should be formed from multiple tubular members having at least one lumen, wherein the rigidity in the proximal part and distal part of the catheter shaft are mutually different, and the rigidity of that proximal part is set higher than that of the distal part. More specifically, catheter shafts wherein the proximal part thereof is configured with a polyimide material as the main component and the distal part thereof is formed from a polymer material having a lower modulus of elasticity than the polyimide, or wherein the proximal part thereof is formed from a metal material and the ,distal part thereof is formed from a polymer material, are highly suitable.
Furthermore, when applying a hydrophilic coating to the distal part of such a catheter shaft, it is preferable to set the hydrophilic coating range so that it extends to the proximal part of the catheter shaft that contacts the distal part thereof, and/or to set the hydrophilic coating range so that it extends to the proximal part of the catheter shaft configured with a larger diameter than the distal part thereof.
Furthermore, in order to adjust the rigidity of the catheter shaft and enhance the controllability of the balloon catheter, the flexibility of the catheter shaft may be varied from the distal part to the proximal part, either in multiple stages or continuously.
Furthermore, in a so-called rapid exchange type balloon catheter wherein the formation of a guide wire lumen for passing the guide wire is limited to extend from the distal end to midway along the catheter shaft, it is preferable that a hydrophilic coating be applied to the outer surface of the catheter shaft from the leading end of the balloon catheter to a site that is more to the proximal side than the back end opening of the guide wire lumen, it being particularly desirable to apply the hydrophilic coating in a range that extends from the farthest end of the balloon catheter to a point that is at least 300 mm on the proximal side thereof.
When applying the hydrophilic coating to the catheter shaft and balloon in the distal part of the balloon catheter, it is better to adjust the thickness of the hydrophilic coating layer on that catheter shaft so that it is greater than the thickness of the hydrophilic coating layer on the balloon and near the balloon, and to adjust the friction resistance of the hydrophilic coating layer of the catheter shaft when wetted so that it is smaller than the friction resistance at the balloon and near the balloon. Here, it is better to adjust the thickness of the hydrophilic coating layer of the catheter shaft to be 2 xcexcm or greater.
Alternatively, such a hydrophilic coating may be applied only to the catheter shaft in the distal part of the balloon catheter.
One method of applying a hydrophilic coating to the balloon catheter in this manner comprises a process step for coating a hydrophilic polymer solution onto the balloon and catheter shaft in the distal part of the balloon catheter, a process step for coating and washing the balloon or the balloon and the vicinity of that balloon with a hydrophilic polymer solution of weaker concentration, and a process step for fixing the hydrophilic polymer to the balloon catheter. Another method comprises a process step for coating a hydrophilic polymer solution onto the balloon and catheter shaft in the distal part of the balloon catheter, a process step for washing the balloon or the balloon and the vicinity of the balloon with a solvent that dissolves that hydrophilic polymer solution, and a process step for fixing the hydrophilic polymer onto the balloon catheter.
Now, in a balloon catheter wherein a metal tubular member is used for at least one of the plurality of tubular members configuring the catheter shaft, in order to prevent a decline in performance due to the plastic deformation of the metal tubular member or members, it is desirable that (1) when such metal tubular member is bent 90 degrees with a radius of curvature that is 50 times the outer diameter thereof, held in that condition for 1 minute, and then released, the bend angle produced in that metal tubular member is 15 degrees or less, or (2) when such metal tubular member is bent 90 degrees with a radius of curvature that is 35 times the outer diameter thereof, held in, that condition for 1 minute, and then released, the bend angle produced in that metal tubular member is 30 degrees or less, or, alternatively, (3) when such metal tubular member is bent 90 degrees with a radius of curvature that is 25 times the outer diameter thereof, held in, that condition for 1 minute, and then released, the bend angle produced in that metal tubular member is 35 degrees or less.
For the material used in such metal tubular members, specifically, materials which contain molybdenum or titanium, or stainless steel selected from among 316 stainless steel, 321 stainless steel, and 430F stainless steel, are preferable.
An example of a favorable form for the balloon described in the foregoing is a balloon having a straight tube part, two conical parts, formed at either end of the straight tube part, tapered so that the diameter thereof becomes increasingly smaller toward the outer end thereof, and two cylindrical sleeve parts formed at the two ends of those conical parts, wherein the skin thickness has been adjusted so that the skin thickness ratio (WB/WA) between the skin thickness of the straight tube part (WA) and the skin thickness of the sleeve part (WB) is less than 2.5 for a balloon nominal expanded diameter of 3.5 mm to 3.0 mm, that skin thickness ratio (WB/WA) is less than 2.3 for a balloon nominal expanded diameter of 2.5 mm, that skin thickness ratio (WB/WA) is less than 2.1 for a balloon nominal expanded diameter of 2.0 mm, and that skin thickness ratio (WB/WA) is less than 2.0 for a balloon nominal expanded diameter of 1.5 mm.
A good raw material for such balloons is a thermoplastic resin exhibiting a Shore hardness greater than 75D, elongation of less than 250%, and a glass transition temperature of less than 37xc2x0 C.
In making the skin thickness thinner in the sleeve part, in particular, it will be well to stretch the tubular member that is the balloon raw material in the axial direction, form it into a balloon by causing it to stretch in the circumferential dimension by blowing, load the straight tube part and conical parts of the balloon into a metal mold while introducing a higher pressure than that occurring during the stretching in the circumferential dimension into the interior of the balloon to thin the skin thickness of the sleeve parts, and stretching the sleeve parts in the axial direction. It is also permissible, however, alternatively to thin the skin thickness of the sleeve parts of the balloon by polishing or grinding.
Furthermore, it is preferable that the balloon described in the foregoing be configured from a polymer material having a crystallized region, and that the crystallinity of the balloon be adjusted to between no less than 10% and no greater than 40%. For a specific method of manufacturing a balloon having such crystallinity as that, first, the balloon is molded by biaxial stretch blow molding a single-lumen tube molded by extrusion molding and exhibiting an elongation of 250 to 450% at the tensile break point, and is then annealed at a temperature that is 10 to 40xc2x0 C. higher than the biaxial stretch blow molding temperature, preferably for 40 to 120 seconds.